Graphic facsimile signals are transmitted both by amplitude modulation (AM) and frequency modulation (FM). In either case the successive instantaneous values of the modulation, that is the amplitude in volts or the frequency in hertz, are detected and used to generate a marking signal applied to a facsimile recorder. Conventional AM and FM detectors have sampled and capacitatively held a number of cycles of the transmitted signal in the process of measuring the amplitude or frequency value. But capacitative circuit components inherently introduce a delay in the detection process, whereas the speeds of facsimile signal transmission and recording are increasing.
It is therefor the object of the present invention to provide electronic apparatus which eliminates capacitative circuitry and the need for sampling multiple cycles of a modulated signal to determine the amplitude or frequency value of its modulation.